1. Field of the Invention
The present invention relates to a system for detecting and controlling a misgrip of a workpiece at the time of feeding workpieces in a transfer press or the like where workpieces are clamped and then transferred into the next machining station by means of transfer bars.
2. Description of the Prior Art
In a prior-art transfer press where works or workpieces are clamped by transfer bars and then transferred to the next machining stations, there are provided workpiece detectors at clamp portions of transfer bars corresponding to each machining station, for detecting the presence or absence of a workpiece at the respective machining station and a workpiece storage circuit for storing workpiece data on the presence or absence of a workpiece at each machining station. If the workpiece data indicate the presence of a workpiece at a machining station but the corresponding workpiece detector does not actually detect the workpiece, then the system will determined that a misgrip takes place.
The prior art system, however, cannot detect such an abnormal condition that the workpiece data indicate the absence of the workpiece but the corresponding workpiece detector is turned on (which means that the workpiece is present), or that a workpiece detector which has been turned on will not be turn off even after the workpiece has been fed into the next machining station and another workpiece was not supplied from the previous machining station.
Further, correction of the workpiece data after the occurence of a misgrip is carried out manually in such a conventional misgrip detecting system and therefore miscorrection of the workpiece data by an operator is likely to occure.
Further, since such a conventional misgrip detecting system does not include means for testing or checking the operation of the system even if a misgrip takes place, the system was sometimes incapable of detecting (or detected errorneously) the misgrip.